sedimentary
Chert (Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs scale; Color: typically gray, white, or beige; Luster: waxy to dull; Structure: microcrystalline; Cleavage: none, exhibits conchoidal fracture; Specific gravity: approx. 2.65.
- Hardness
- 7 Mohs scale
- Color
- typically gray, white, or beige
- Luster
- waxy to dull
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Physical properties
Hardness: 7 Mohs scale; Color: typically gray, white, or beige; Luster: waxy to dull; Structure: microcrystalline; Cleavage: none, exhibits conchoidal fracture; Specific gravity: approx. 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine or freshwater environments. Most specimens are millions of years old, often found in limestone or chalk beds.
Uses & applications
Historically used for stone tools/weapons; modernly used as road aggregate, architectural stone, and in spark-lighting mechanisms (flint).
Geological facts
Chert has been used by humans for over 2 million years to create sharp-edged tools because of its predictable fracture pattern. Some banded varieties are sold as decorative river rocks.
Field identification & locations
Identify in the field by its hardness (scratches glass), waxy appearance, and very sharp, curved (conchoidal) edges when broken. Commonly found in stream beds or eroded from limestone outcrops.
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